is it necessary? my old downstream one was throwing a CEL, and i was getting horrible mileage, so i replaced it with a DENSO one, and i torqued it to about 30 ft/ibs and used the liquid stuff it came with to put on the threads, and i still have a feeling im getting bad mileage. so is it because i need to reset my ECU or what?

thanks

 

ok, i used some gumout fuel system cleaner now when i filled up my tank to the top, so well see how this goes.

 

resetting the ECU after any sensor change is always a good idea.
No you don't have to do it, but if you'd like the ECU to use the new O2 correctly right away you should.

 

Ok, how do i reset it properly? im not good with eletric stuff, need detailed instructions lol

thanks

 

remove negative terminal of battery.
count to 10 slowly.
reconnect battery terminal.
Start car and let idle for 15 minutes.
Switch off car.
done.

If you're OBD2 you will have to drive the car for a couple days to clear the readynesss flags to be emissions legit.